That may be true, but we're in a different velocity range here, so I don't think the comparison stands. Humanity wastes a heck of a lot of energy fighting drag in general, if there was any benefit of dimples on objects travelling at high subsonic velocities, airliners would be covered in them

Ultimately, if you want the ultimate destructive performance without changing any of the launcher specs, you should go for steel BBs.

I find that using HPA lets even plastic BBs be pretty destructive though, this is with 0.25g plastic BBs with 850 psi behind them: